Without giving too much away to its 15 million viewers, the episode will feature members of the Tilsley family from No 5 in a flutter; Ivy Tilsley, a shark lass with strong trade union loyalties, will get an offer from Mike Baldwin, anti-union boss of the denim factory where she works. Eric Rosser, the programme's official archivist, described it last week as "a tidy episode – a few answers, as usual, and a few questions to keep up interest".

Mr Rosser, a 56-year-old former Inland Revenue official, has an extraordinary attachment to Coronation Street, which began on 9 December 1960. He watched it from a bed in Manchester Royal Infirmary.

He spent the next 10 years studying the serial, absorbing the characters. Eventually, Mr Rosser was hired as a full-time historian, cartographer and memory man. "I'm one of the people Coronation Street has been very good for," he said. "It's something familiar, yet just that little bit different, like having friends who surprise you."

Among the millions who relish the series with him are Sir John Betjeman, the poet laureate, who described it as "the Pickwick Papers of television".

The serial was devised by Tony Warren. He wanted to call it "Florizel Street", but the programme planners rejected the title because Florizel sounded like a detergent.

His original characters were based on people observed on a long crawl through north-west pubs. Five of them survive to appear this week, including Ena Sharples, all hard edge and grumpy compassion, and Elsie Tanner, the drinking man's crumpet.

The set for Coronation Street was based on Archie Street, Salford, which comprised, before it was demolished, 10 houses on one side, six on the other, and an off-licence. Only one of the houses had a bath.

Critics argue that, for all its surface reality, issues of concern to real working-class northerners are only touched upon. The working-class racialism that disturbs community workers in the north-west is never examined. Emily and Ernest Bishop fostered two black children for Christmas, and Ray Langton left No 5 to go to Holland after an affair with a black waitress. There would have been more ripples in Salford.

Stan Barstow, the novelist whose work is distinguished by faithful recording of working-class ways, summed it up best when he said: "It never has any smell of evil about it."

But Mr Rosser is content. "It's a family show," he said, "and you don't want to touch some things – abortion's an example. There are people who wouldn't want to identify with that. We like things to come out right in the end after all."

This is an edited extract

***This article was amended on 12 June 2013. An earlier headline said From the Observer archive, 1 June 1988. The date should have been 1 June 1980. Many thanks to cymru1489 for pointing out the error.